The head portion of a ring wrench or socket usually has an inner shape and size complementary to that of a typically hexagonal fastener head. The head of such a wrench has an inner surface, which surrounds the fastener head with only a small amount of play between the inner surface of the wrench or socket and the fastener head. As torque is applied to the wrench or socket the torque is transmitted to the fastener head to turn the fastener in the appropriate direction.
Ring-type sockets and wrenches are preferable to open jaw type wrenches and sockets as the torque applied to the wrench is transmitted to the fastener via a much larger contact area and the ring head of the socket or wrench Ring-type sockets and wrenches can also transmit far greater torque without harmful distortion of the fastener head and with less chance of the wrench or socket slipping off the fastener. However, if incorrectly sized, poor quality or open wrench has been used on a stubborn or tight fastener and the fastener head has become inoperable by reason of damage or corrosion, the fastener would normally require to be removed by other means than a socket or wrench. A further problem is that sometimes when using a wrench further purchase power may be required to tighten or slacken a fastener. Ring wrenches or sockets however can seldom be used to operate damaged or rounded fasteners, in particular those in recessed areas where the space surrounding the fastener head is restricted. Torque tightening wrenches which can operate partially rounded fasteners are known, but these normally require unrestricted access to the fastener head. These wrenches/sockets are incapable of operating severely damaged or worn fastener heads.